230. Kth Smallest Element in a BST

[Shawngbk]

使用中序遍历复杂度O（n）

/**

• Definition for a binary tree node.
• public class TreeNode {
• int val;
• TreeNode left;
• TreeNode right;
• TreeNode(int x) { val = x; }
• } */ public class Solution { public int kthSmallest(TreeNode root, int k) { List list = new ArrayList(); helper(root, list); return list.get(k-1); } private void helper(TreeNode root, List list) { if(root != null) { if(root.left != null) { helper(root.left, list); } list.add(root.val); if(root.right != null) { helper(root.right, list); } } } }

[Shawngbk]